Polyvinyl chloride special material for elbow pipe and preparation method thereof

Abstract

The application discloses a special polyvinyl chloride elbow pipe material and a preparation method thereof. The special polyvinyl chloride elbow pipe material comprises the following raw materials: polyvinyl chloride resin, acrylic ester copolymer, modifier, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, modified nano silicon dioxide, heat stabilizer and lubricant. The special polyvinyl chloride elbow pipe material has high tensile elongation at break and high compressive buckling strain in the medium-temperature bending interval of 80-100 DEG C, and fundamentally solves the problems of 'outer wall cracking and inner wall wrinkling' of the existing PVC material in the medium-temperature bending forming.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and specifically relates to a special material for polyvinyl chloride (PVC) pipe bending and its preparation method. Background Technology

[0002] Polyvinyl chloride (PVC) pipes are widely used in building water supply and drainage, chemical fluid transportation, agricultural irrigation, and electrical conduit due to their low cost, chemical corrosion resistance, and good processing performance. In recent years, with the promotion of prefabricated buildings and the development of customized pipe networks, the market demand for non-standard angles, large diameters, and thin-walled bends has become increasingly urgent. In industrial production, a medium-temperature bending process is commonly used—heating the pipe to be bent to 80-100℃ (near the glass transition temperature of PVC). At this temperature, PVC has sufficient plastic deformation capacity to adapt to bending, while not collapsing due to excessive softening, thus making it the preferred temperature window for pipe bending.

[0003] However, this process has long faced two major technical challenges in actual production, resulting in consistently high scrap rates: First, there is tensile cracking on the outer wall of the bent pipe: During the bending process, the outer side of the bent pipe is subjected to tensile stress, resulting in a reduction in the wall thickness. When the tensile strain exceeds the material's elongation at break, the outer wall will exhibit surface whitening, silvering, or even penetrating cracks. This problem is particularly prominent in low-temperature workshop environments during winter, in situations with high bending speeds, or in thin-walled pipes (wall thickness less than 4mm), and in severe cases, the scrap rate can reach over 20%.

[0004] Secondly, there is the issue of compression folding on the inner wall of the bend: During bending, the inner side of the bend is subjected to compressive stress. When the compressive strain exceeds the material's critical buckling strain, wavy wrinkles or even microcracks will appear on the inner wall. These wrinkles not only affect the fluid flowability and the aesthetics of the pipe, but may also gradually develop into through-cracks during long-term pressure use, causing leakage accidents. This problem is most common in large-diameter pipes (≥160mm), small bending radii (less than twice the pipe diameter), or thick-walled pipes (wall thickness ≥8mm), and is a key bottleneck restricting the production of large-diameter PVC bends.

[0005] In existing technologies, several solutions have been proposed to address the cracking or deformation problems that occur when pipes are bent. For example, some researchers have improved bending resistance by adding protective layers or reinforcing lines inside and outside the pipe, while others have released bending stress by creating stress grooves in the inner wall of the hose. Still others have prevented dents by controlling axial material feeding at both ends during hydroforming. However, these solutions either involve changes to the pipe structure, requiring modifications to the extrusion die or the addition of a composite process, or they are mainly designed for metal pipes or rubber hoses and are difficult to directly apply to the material modification of PVC bends.

[0006] In summary, a long-standing unresolved technical contradiction exists in this field: increasing the elongation at break of a material (to avoid outer wall cracking) typically reduces the material's elastic modulus and compressive buckling resistance; while increasing compressive resistance (to avoid inner wall wrinkling) often comes at the cost of sacrificing tensile ductility. This trade-off makes developing a PVC-specific material that can simultaneously achieve high tensile elongation at break and high compressive buckling strain at 80-100℃ a recognized technical challenge in the industry. Summary of the Invention

[0007] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a special material for PVC pipe bending and its preparation method. This special material for PVC pipe bending has both high tensile elongation at break (≥180%) and high compressive buckling strain (≥35%) in the medium-temperature bending range of 80-100℃, fundamentally solving the problem of "outer wall cracking and inner wall wrinkling" in existing PVC materials during medium-temperature bending molding.

[0008] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A special material for PVC pipe bending includes the following raw materials: PVC resin, acrylate copolymer, modifier, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, modified nano silica, heat stabilizer, and lubricant.

[0009] In some embodiments of the present invention, the special material for PVC bend pipes comprises the following raw materials in parts by weight: PVC resin: 90-120 parts; acrylate copolymer: 3.5-6 parts; modifier: 10-18 parts; ethylene-methyl acrylate-glycidyl methacrylate terpolymer: 2-6 parts; nano silica: 3-8 parts; heat stabilizer: 3.7-6 parts; lubricant: 0.8-2 parts.

[0010] In some embodiments of the present invention, the degree of polymerization of the polyvinyl chloride resin is 1100-1350.

[0011] In some embodiments of the present invention, the acrylate copolymer is composed of acrylate copolymer A and acrylate copolymer B in a weight ratio of (2-3.5):(1.5-2.5), wherein the weight average molecular weight of acrylate copolymer A is 1.2 million to 2 million, and the weight average molecular weight of acrylate copolymer B is 300,000 to 500,000.

[0012] In some embodiments of the present invention, the modifier is a three-layer core-shell structure impact modifier, wherein the three-layer core-shell structure impact modifier comprises, from the inside out, a polybutadiene rubber core layer, a polybutadiene-styrene gradient transition layer, and a polymethyl methacrylate shell layer, wherein the polybutadiene rubber core layer accounts for 45%-55% of the total mass of the modifier, the polybutadiene-styrene gradient transition layer accounts for 20%-30% of the total mass of the modifier, and the polymethyl methacrylate shell layer accounts for 20%-30% of the total mass of the modifier; the styrene content in the polybutadiene-styrene gradient transition layer increases radially from 0% to 40-60% from the inside out; and the weight-average molecular weight of the polymethyl methacrylate shell layer is 80,000-150,000.

[0013] In some embodiments of the present invention, the three-layer core-shell structure impact modifier is obtained by a preparation method comprising the following steps: (1) Butadiene monomer is polymerized in the presence of an initiator to obtain a polybutadiene rubber core layer; (2) Add a mixture of styrene and butadiene monomers continuously to the core layer emulsion obtained in step (1). During the addition process, the mass ratio of styrene to the mixture increases linearly from 0% to 40-60%, and a gradient transition layer with styrene content continuously increasing in the radial direction is formed by polymerization. (3) Add methyl methacrylate monomer to the product obtained in step (2) and polymerize to form a polymethyl methacrylate shell; (4) Spray drying yields a three-layer core-shell structure impact modifier.

[0014] In some embodiments of the present invention, the particle size of the three-layer core-shell structure impact modifier is 350-550 nm.

[0015] In some embodiments of the present invention, the ethylene-methyl acrylate-glycidyl methacrylate terpolymer has a melt index of 3-10 g / 10 min at 190°C / 2.16 kg.

[0016] In some embodiments of the present invention, the glycidyl methacrylate content in the ethylene-methyl acrylate-glycidyl methacrylate terpolymer is 5wt%-12wt%.

[0017] In some embodiments of the present invention, the modified nano-silica is methyl methacrylate-grafted nano-silica, the grafting rate of the methyl methacrylate-grafted nano-silica is 6wt%-12wt%, and the degree of polymerization of the polymethyl methacrylate graft layer of the methyl methacrylate-grafted nano-silica is 20-80.

[0018] In some embodiments of the present invention, the method for preparing methyl methacrylate-grafted nano-silica includes the following steps: reacting nano-silica with a silane coupling agent to obtain double-bond functionalized silica; then reacting it with an initiator to fix the initiator on the surface; adding methyl methacrylate monomer for in-situ polymerization to obtain methyl methacrylate-grafted nano-silica.

[0019] In some embodiments of the present invention, the original particle size of the modified nano-silica is 15-40 nm.

[0020] In some embodiments of the present invention, the heat stabilizer is composed of a liquid phosphite-calcium-zinc composite stabilizer and a β-diketone auxiliary stabilizer in a weight ratio of (3.5-5.5):(0.2-0.5).

[0021] In some embodiments of the present invention, the liquid phosphite-calcium-zinc composite stabilizer is composed of trinonylphenyl phosphite, calcium stearate, zinc stearate and pentaerythritol in a mass ratio of (10-20):(30-50):(20-40):(10-20).

[0022] In some embodiments of the present invention, the lubricant is composed of oxidized polyethylene wax and fatty acid amide in a weight ratio of (0.5-1.2):(0.3-0.8).

[0023] A method for preparing a special material for PVC bend pipes as described above includes the following steps: (1) Mix polyvinyl chloride resin with heat stabilizer once, then add lubricant and mix twice, then add acrylate copolymer, modifier, ethylene-methyl acrylate-glycidyl methacrylate terpolymer and modified nano silica and mix three times to obtain a mixture; (2) The mixture obtained in step (1) is melt-extruded and granulated to obtain the final product.

[0024] In some embodiments of the present invention, in step (1), the first mixing is carried out by stirring at 75-85°C for 8-12 minutes at a mixing speed of 600-1200 rpm.

[0025] In some embodiments of the present invention, in step (1), the secondary mixing is carried out by stirring at 90-100°C for 5-8 minutes at a mixing speed of 600-1200 rpm.

[0026] In some embodiments of the present invention, in step (1), the three mixing steps are performed by stirring at 70-80°C for 8-12 minutes at a mixing speed of 200-400 rpm.

[0027] In some embodiments of the present invention, in step (2), the equipment used for melt extrusion granulation is a twin-screw extruder, and the parameters of melt extrusion granulation are: zone 1 temperature 140-150℃, zone 2 temperature 155-165℃, zone 3 temperature 165-170℃, zone 4 temperature 165-170℃, die head temperature 160-165℃, and screw speed 250-350rpm.

[0028] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe, and then heating the straight pipe to 80-100°C on a bending device to bend it into shape.

[0029] The inner bend surface of the PVC bend has no visible wrinkles or microcracks under a 20x stereomicroscope, and the outer bend surface has no tensile whitening or cracking. The maximum wall thickness reduction rate of the bend section is ≤8%, and the drop hammer impact fracture rate at -5℃ is ≤3%.

[0030] The beneficial effects of this invention are: (1) The polyvinyl chloride pipe bending material of the present invention has both high tensile elongation at break and high compressive buckling strain in the medium temperature bending range of 80-100℃, which fundamentally solves the problem of "outer wall cracking and inner wall wrinkling" of existing PVC materials when bending and molding at medium temperature. (2) The polyvinyl chloride pipe bending material of the present invention uses a specific acrylate copolymer, a modifier, an ethylene-methyl acrylate-glycidyl methacrylate terpolymer and modified nano silica. The four raw materials work synergistically to make the pipe material prepared achieve ≥180% elongation at break (tensile side) and ≥35% compressive buckling strain (compression side). (3) The modifier in the special material for PVC bend pipe of the present invention is a three-layer core-shell structure impact modifier, which breaks through the two-layer structure of conventional methyl methacrylate-butadiene-styrene copolymer, so that the compressive buckling strain of the material increases from 20%-25% of the ordinary system to 35%-42%, and the compression recovery rate increases from less than 30% to more than 70%. (4) The special material for PVC bend pipe of the present invention contains epoxy functional group reactive terpolymer ethylene-methyl acrylate-glycidyl methacrylate terpolymer, which utilizes its chemical reaction with PVC and modified nano silica to construct a "polymer grafted particle-matrix" chemical crosslinking network, and inhibits the initiation of microcracks through stress buffering and interface enhancement dual mechanisms. (5) In the polyvinyl chloride pipe bending material of the present invention, by using methyl methacrylate grafted nano silica, the advantages of rigid particles induced silver crack toughening are brought into play, and the interface debonding and agglomeration are avoided through the grafted layer. The bending modulus at 80-100℃ is precisely controlled in the "golden window" of 800-1200MPa, thus achieving a balance between rigidity and toughness. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments.

[0032] Example 1: A special material for PVC pipe bending, comprising the following raw materials:

[0033] The three-layer core-shell structure impact modifier was prepared using a seed emulsion polymerization method, with the specific steps as follows: (1) Preparation of polybutadiene rubber core layer In a 2L high-pressure reactor equipped with a stirrer, thermometer, condenser, and nitrogen inlet, 800g of deionized water, 12g of sodium dodecyl sulfate, 2.4g of potassium persulfate, and 1.6g of sodium bicarbonate were added sequentially. After stirring and dissolving, 480g of butadiene monomer was added, and stirring was started at 250 rpm. Nitrogen gas was purged for 30 minutes to remove oxygen. The temperature was raised to 65℃ and maintained for polymerization for 8 hours. Samples were taken to determine the conversion rate. When the conversion rate was ≥95%, the reaction was stopped, yielding a polybutadiene rubber core emulsion with a solid content of approximately 35-40% and an average latex particle size of 300-450nm (measured by dynamic light scattering). (2) Synthesis of gradient transition layer Add a mixture of styrene and butadiene monomers continuously to the polybutadiene core emulsion obtained in step (1) using a metering pump. The total adding time is 90 minutes and the total amount of the mixed monomers is 240g. During the adding process, the flow ratio of the two metering pumps is controlled by a programmable controller so that the mass fraction of styrene in the mixed monomers increases linearly with the adding time, specifically: f(t) = (t / 90) × 50%.

[0034] Where t is the time (in minutes) after the start of the dripping, that is: t=0 minutes (at the start of dropping): Styrene ratio = 0%, Butadiene ratio = 100% t=45 minutes (midpoint): Styrene ratio = 25%, Butadiene ratio = 75% t=90 minutes (at the end): Styrene ratio = 50%, Butadiene ratio = 50% Because the monomers polymerize rapidly after entering the reaction system (half-life of about 5-10 minutes), the copolymer layers formed by polymerization at different time periods have different styrene contents, and are deposited from the inside to the outside in the order of polymerization time. Therefore, in the final transition layer, the styrene content increases continuously from 0% to 50% radially from the inside to the outside (target range 40-60%). During the dropwise addition, the initiator solution (0.8 g potassium persulfate dissolved in 20 g water) was added simultaneously at a rate of 0.22 g / min. After the dropwise addition was completed, the reaction was kept at the temperature for another 2 hours to ensure that the monomer conversion rate was ≥98%. (3) Preparation of polymethyl methacrylate shell Add 240g of methyl methacrylate (MMA) monomer to the reaction system in step (2), and simultaneously add 0.4g of potassium persulfate (dissolved in 10g of deionized water) as initiator. Heat to 75℃ and maintain the temperature for 4 hours for polymerization. The conversion rate is ≥98%. (4) Post-processing The emulsion obtained in step (3) was spray-dried at an inlet air temperature of 180°C and an outlet air temperature of 80°C to obtain a white powdery three-layer core-shell structure impact modifier. Alternatively, the emulsion was demulsified (by adding 1% calcium chloride solution), filtered, washed, vacuum-dried at 60°C for 24 hours, and then pulverized through a 200-mesh sieve. Dynamic light scattering analysis showed that the average particle size of the obtained three-layer core-shell structure impact modifier was 450 nm, the polydispersity index (PDI) was 0.10, and differential scanning calorimetry (DSC, heating rate 10 °C / min) showed that the core layer had a Tg of -85 °C, the transition layer exhibited a broad glass transition temperature range of -75 °C to +55 °C, and the shell layer had a Tg of 118 °C.

[0035] A method for preparing methyl methacrylate-grafted nano-silica includes the following steps: reacting nano-silica with silane coupling agent KH570 to obtain double-bond functionalized silica; then reacting it with initiator AIBN to fix the initiator on the surface; adding methyl methacrylate monomer for in-situ polymerization to obtain methyl methacrylate-grafted nano-silica. By controlling the amount of monomer and the reaction time, the grafting rate is 9 wt% and the degree of polymerization of the grafted chain is 51.

[0036] A method for preparing a special material for PVC bend pipes as described above includes the following steps: (1) Add polyvinyl chloride resin, liquid phosphite-calcium zinc composite stabilizer and β-diketone auxiliary stabilizer into a high-speed mixer and stir at 900 rpm for 10 minutes at 80°C; (2) Add oxidized polyethylene wax and fatty acid amide, and stir at 900 rpm for 6 minutes at 95°C; (3) Cool down to 75°C, and add acrylate copolymer A, acrylate copolymer B, three-layer core-shell structure impact modifier, ethylene-methyl acrylate-glycidyl methacrylate terpolymer and methyl methacrylate grafted nano silica in sequence. Stir at 300 rpm for 10 minutes at 75°C. (4) Cool the mixture to below 40°C and then melt-extrude and granulate it using a parallel twin-screw extruder. The temperature of the extruder is 145°C in zone 1, 160°C in zone 2, 168°C in zone 3, 168°C in zone 4, 162°C at the die head, and the screw speed is 300 rpm to obtain a special material for PVC pipe bending.

[0037] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ200×6.8mm, heating the straight pipe to 90°C on a bending device, and bending it to 135° at a speed of 5mm / s with a bending radius of 400mm.

[0038] Test results: The maximum thinning rate of the outer wall was 7.2%. No wrinkles or microcracks were found on the inner wall under a 20x microscope. The wall was unbroken after 10 drops of a drop hammer at -5℃. The specific test items and methods are as follows, and the specific test results are shown in Table 1.

[0039] Maximum thinning rate of outer wall: Measured using an ultrasonic thickness gauge or a terahertz thickness gauge (accuracy 0.01mm). Before measurement, three measurement points are evenly selected circumferentially on the straight pipe section before bending. The average wall thickness is taken as the original wall thickness δ0. After bending, a measurement point is selected every 20mm along the center line of the outer arc apex of the bent section from the bending start point to the bending end point. The wall thickness at each point is measured, and the minimum value among all measurement points is taken as the minimum wall thickness δmin. The maximum thinning rate is calculated using the following formula: Thinning rate = (δ0 - δmin) / δ0 * 100%. Elongation at break: The special material is hot-pressed into a 4mm thick plate, cut into ISO 527-21A dumbbell-shaped specimens, and then balanced at 80℃, 90℃, and 100℃ for 10 minutes using a universal testing machine (with an environmental chamber). The elongation at break is then tested at a tensile speed of 50mm / min. Five parallel samples are tested at each temperature, and the average value is taken. Compression buckling strain and compression recovery rate: A cylindrical specimen with a diameter of 25 mm and a height of 50 mm was injection molded from the special material. A compression test was conducted at 90℃ using a universal testing machine at a compression rate of 5 mm / min. The stress-strain curve was recorded. The compression buckling strain was defined as the strain at the first peak of the curve or the first wrinkle on the specimen surface. After unloading, the compression recovery rate was calculated using the formula. Flexural modulus: A strip specimen with a length of 80 mm × 10 mm × 4 mm was injection molded from the special material. A three-point bending test was conducted at 90℃ (span 64 mm, test speed 2 mm / min), and the flexural modulus was recorded.

[0040] Table 1.

[0041] The above results show that the PVC pipe bending material of this embodiment has both high tensile elongation at break (≥180%) and high compressive buckling strain (≥35%) in the medium temperature bending range of 80-100℃, compression recovery rate ≥70%, and flexural modulus in the range of 800-1200MPa. After the pipe is bent, there is no crack on the outer wall and no wrinkles on the inner wall.

[0042] Example 2: The special material for PVC bends and its preparation method are exactly the same as those in Example 1, except that the preparation method of the PVC bends is different.

[0043] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ315×9.2mm, heating the straight pipe to 95° on a bending device, and bending it to 95° at a speed of 5mm / s with a bending radius of 630mm.

[0044] Test results: The maximum thinning rate of the outer wall was 7.8%, and there were no wrinkles or microcracks on the inner wall under a 20x microscope. The wall was unbroken after 10 drops of a drop hammer at -5℃. The specific test results are shown in Table 2 below.

[0045] Table 2.

[0046] Example 3: A special material for PVC pipe bending, comprising the following raw materials:

[0047] The preparation method of the three-layer core-shell structure impact modifier and methyl methacrylate-grafted nano-silica is the same as in Example 1.

[0048] The preparation method of the special material for PVC bend pipes as described above is exactly the same as that in Example 1.

[0049] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ110×4.5mm, heating the straight pipe to 85°C on a bending device, and bending it to 180° at a speed of 5mm / s with a bending radius of 165mm.

[0050] Test results: The maximum thinning rate of the outer wall is 7%. No wrinkles or microcracks were found on the inner wall under a 20x microscope. The wall was unbroken after 10 drops of a drop hammer at -5℃. The specific test results are shown in Table 3 below.

[0051] Table 3.

[0052] Comparative Example 1: (Compared to Example 1, the raw material for PVC bend pipes contains only 4.8 parts of acrylate copolymer A and no acrylate copolymer B) A special material for PVC pipe bending, comprising the following raw materials:

[0053] The preparation method of the three-layer core-shell structure impact modifier and methyl methacrylate-grafted nano-silica is the same as in Example 1.

[0054] The preparation method of the special material for PVC bend pipes as described above is exactly the same as that in Example 1.

[0055] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ200×6.8mm, heating the straight pipe to 90°C on a bending device, and bending it to 135° at a speed of 5mm / s with a bending radius of 400mm.

[0056] Test results: The extrusion torque was significantly too high, the surface of the extruded pipe was rough, the outer wall showed obvious stretching and whitening when bent, the maximum thinning rate was 14.5%, and multiple microcracks were observed on the inner wall under a 20x microscope, which is unqualified.

[0057] This comparative example demonstrates that although using only high-molecular-weight acrylate copolymer A can improve melt strength, its processing fluidity is too poor, and the stress distribution is uneven when the material is bent, making it impossible to effectively avoid cracking of the outer wall.

[0058] Comparative Example 2: (Compared to Example 1, the raw material for PVC bend pipes contains only 4.8 parts of acrylate copolymer B, and no acrylate copolymer A) A special material for PVC pipe bending, comprising the following raw materials:

[0059] The preparation method of the three-layer core-shell structure impact modifier and methyl methacrylate-grafted nano-silica is the same as in Example 1.

[0060] The preparation method of the special material for PVC bend pipes as described above is exactly the same as that in Example 1.

[0061] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ200×6.8mm, heating the straight pipe to 90°C on a bending device, and bending it to 135° at a speed of 5mm / s with a bending radius of 400mm.

[0062] Test results: The elongation at break at 90℃ was only 115%, far below the target value of 180%. Significant tensile cracking occurred on the outer wall during bending, indicating it is substandard.

[0063] This comparative example demonstrates that although medium molecular weight acrylate copolymer B has good processing fluidity, its melt strength is insufficient, and it cannot provide strain hardening effect under tension, resulting in a high risk of outer wall cracking.

[0064] Comparative Example 3: (Compared with Example 1, the three-layer core-shell structure impact modifier in the PVC pipe bending material was adjusted to a two-layer core-shell structure methyl methacrylate-butadiene-styrene copolymer) A special material for PVC pipe bending, comprising the following raw materials:

[0065] A method for preparing methyl methacrylate-butadiene-styrene copolymer includes the following steps: (1) Core layer synthesis: Butadiene monomers were polymerized at 65°C for 8 hours in the presence of emulsifier and initiator to obtain polybutadiene rubber core emulsion with a particle size of about 200 nm; (2) Shell grafting: Add a mixture of styrene and methyl methacrylate monomers (mass ratio 1:1) to the core emulsion, add an initiator, and polymerize at 70°C for 4 hours to form a shell coating, thus obtaining a two-layer core-shell structure methyl methacrylate-butadiene-styrene copolymer with a core-shell ratio of 70:30.

[0066] The core layer of this methyl methacrylate-butadiene-styrene copolymer is polybutadiene, and the shell layer is styrene-methyl methacrylate copolymer. The composition between the core layer and the shell layer is abrupt, with no gradient transition layer.

[0067] The preparation method of methyl methacrylate-grafted nano-silica is the same as that in Example 1.

[0068] A method for preparing a special material for PVC bend pipes as described above includes the following steps: The preparation method of the special material for PVC bend pipes as described above is exactly the same as that in Example 1.

[0069] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ200×6.8mm, heating the straight pipe to 90°C on a bending device, and bending it to 135° at a speed of 5mm / s with a bending radius of 400mm.

[0070] Test results: The compressive buckling strain decreased to 22%. After bending, obvious wavy wrinkles appeared on the inner wall, with a depth of about 0.3 mm. Microcracks were visible at the crests of the wrinkles under a 20x microscope, which is unacceptable.

[0071] This comparative example demonstrates that conventional two-layer core-shell structured methyl methacrylate-butadiene-styrene copolymers cannot effectively resist compressive stress. During compression, stress concentration easily occurs at the core-shell interface, leading to wrinkles on the inner wall.

[0072] Comparative Example 4: A special material for PVC pipe bending includes the following raw materials: (Compared with Example 1, the raw materials for PVC pipe bending do not contain ethylene-methyl acrylate-glycidyl methacrylate terpolymer)

[0073] The preparation method of the three-layer core-shell structure impact modifier and methyl methacrylate-grafted nano-silica is the same as in Example 1.

[0074] The preparation method of the special material for PVC bend pipes as described above is exactly the same as that in Example 1.

[0075] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ200×6.8mm, heating the straight pipe to 90°C on a bending device, and bending it to 135° at a speed of 5mm / s with a bending radius of 400mm.

[0076] Test results: Multiple fine microcracks (1-3 mm in length) appeared on the outer wall during bending, and the fracture rate was 15% under drop hammer impact at -5℃. Microscopic observation showed that the cracks originated from the outer wall surface and propagated along the tensile direction.

[0077] This comparative example demonstrates that the stress buffering effect of the ethylene-methyl acrylate-glycidyl methacrylate terpolymer is indispensable. Without this component, bending stress cannot be effectively dissipated, leading to the initiation and propagation of microcracks.

[0078] Comparative Example 5: (Compared with Example 1, the raw material for PVC bend pipe uses ungrafted ordinary nano-silica) A special material for PVC pipe bending, comprising the following raw materials:

[0079] The preparation method of the three-layer core-shell structure impact modifier is the same as that in Example 1.

[0080] The preparation method of the special material for PVC bend pipes as described above is exactly the same as that in Example 1.

[0081] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ200×6.8mm, heating the straight pipe to 90°C on a bending device, and bending it to 135° at a speed of 5mm / s with a bending radius of 400mm.

[0082] Test results: The nano-silica particles clearly agglomerated in the matrix, resulting in pitted defects on the pipe surface. During bending, stress concentration points formed around the agglomerated particles, leading to localized cracking, rendering the pipe unqualified.

[0083] This comparative example demonstrates that unmodified nano-silica cannot be uniformly dispersed in PVC and instead becomes a source of defects.

[0084] Comparative Example 6: (Compared with Example 1, ordinary nano-calcium carbonate was used instead of methyl methacrylate-grafted nano-silica in the raw material for PVC pipe bending.) A special material for PVC pipe bending, comprising the following raw materials:

[0085] The preparation method of the three-layer core-shell structure impact modifier is the same as that in Example 1.

[0086] The preparation method of the special material for PVC bend pipes as described above is exactly the same as that in Example 1.

[0087] A method for preparing a polyvinyl chloride (PVC) bend pipe involves extruding the PVC bend pipe material as described above into a straight pipe with a diameter of φ200×6.8mm, heating the straight pipe to 90°C on a bending device, and bending it to 135° at a speed of 5mm / s with a bending radius of 400mm.

[0088] Test results: The flexural modulus at 90℃ dropped to 680MPa, the bent tube rebounded severely, the bending angle deviation reached 7°, and the wall thickness unevenness increased, indicating that ordinary nano-calcium cannot effectively control the flexural modulus to the ideal range.

[0089] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A special material for bending polyvinyl chloride pipes, characterized in that: The raw materials include: polyvinyl chloride resin, acrylate copolymer, modifier, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, modified nano silica, heat stabilizer, and lubricant.

2. The special material for PVC pipe bending according to claim 1, characterized in that: The raw materials include the following parts by weight: polyvinyl chloride resin: 90-120 parts; acrylate copolymer: 3.5-6 parts; modifier: 10-18 parts; ethylene-methyl acrylate-glycidyl methacrylate terpolymer: 2-6 parts; nano silica: 3-8 parts; heat stabilizer: 3.7-6 parts; Lubricant: 0.8-2 parts.

3. The special material for PVC pipe bending according to claim 1, characterized in that: The acrylate copolymer is composed of acrylate copolymer A and acrylate copolymer B in a weight ratio of (2-3.5):(1.5-2.5), wherein the weight average molecular weight of acrylate copolymer A is 1.2 million to 2 million, and the weight average molecular weight of acrylate copolymer B is 300,000 to 500,000.

4. The special material for PVC pipe bending according to claim 1, characterized in that: The modifier is a three-layer core-shell structure impact modifier, which consists of a polybutadiene rubber core layer, a polybutadiene-styrene gradient transition layer, and a polymethyl methacrylate shell layer from the inside out. The polybutadiene rubber core layer accounts for 45%-55% of the total mass of the modifier, the polybutadiene-styrene gradient transition layer accounts for 20%-30% of the total mass of the modifier, and the polymethyl methacrylate shell layer accounts for 20%-30% of the total mass of the modifier. The styrene content in the polybutadiene-styrene gradient transition layer increases continuously from 0% to 40-60% radially from the inside out. The weight-average molecular weight of the polymethyl methacrylate shell layer is 80,000-150,000.

5. The special material for PVC pipe bending according to claim 4, characterized in that: The particle size of the three-layer core-shell structure impact modifier is 350-550 nm.

6. The special material for PVC pipe bending according to claim 1, characterized in that: The ethylene-methyl acrylate-glycidyl methacrylate terpolymer has a melt index of 3-10 g / 10 min at 190℃ / 2.16 kg.

7. The special material for PVC pipe bending according to claim 1, characterized in that: The modified nano-silica is methyl methacrylate-grafted nano-silica, the grafting rate of the methyl methacrylate-grafted nano-silica is 6wt%-12wt%, and the degree of polymerization of the polymethyl methacrylate graft layer of the methyl methacrylate-grafted nano-silica is 20-80.

8. The special material for PVC pipe bending according to claim 1, characterized in that: The heat stabilizer is composed of a liquid phosphite-calcium-zinc composite stabilizer and a β-diketone auxiliary stabilizer in a weight ratio of (3.5-5.5):(0.2-0.5).

9. A method for preparing a special material for polyvinyl chloride (PVC) pipe bending as described in any one of claims 1 to 8, characterized in that: Includes the following steps: (1) Mix polyvinyl chloride resin with heat stabilizer once, then add lubricant and mix twice, then add acrylate copolymer, modifier, ethylene-methyl acrylate-glycidyl methacrylate terpolymer and modified nano silica and mix three times to obtain a mixture; (2) The mixture obtained in step (1) is melt-extruded and granulated to obtain the final product.

10. A method for preparing a polyvinyl chloride (PVC) bend, characterized in that, The polyvinyl chloride pipe bending material according to any one of claims 1-8 is extruded into a straight pipe, and the straight pipe is heated to 80-100°C on a bending device and bent to obtain the pipe.

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